U.S. Pat. No. 4,055,705 to Stecura et al discloses a ceramic thermal barrier coating system in which NiCrAlY is covered with a reflective oxide, such as ZrO.sub.2 --Y.sub.2 O.sub.3 or ZrO.sub.2 --MgO. The NiCrAlY has a thickness between 3 mils and 7 mils, and the coating is between 10 mils and 30 mils thick.
U.S. Pat. No. 4,248,940 to Goward et al is concerned with a thermal barrier coating for use on nickel or chromium alloy materials. The MCrAlY's are applied in a graded fashion from 100% metal at the metal coating interface to 100% coating on the surface. The patentee states this reduces problems associated with thermal shock due to material expansion.
U.S. Pat. No. 4,852,542 to Kamo et al sets forth several advantages and drawbacks of various ceramic coatings for use in engines. The thin coatings fail to provide sufficient heat buildup in the combustion chamber which is necessary for increased engine efficiency. Thick coatings add greatly to thermal efficiency, but cause over-heating resulting in increased maintenance and reduced life expectancy. The patentee proposes a coating not less than 2 mils or greater than 9 mils thick.